Low friction camshaft with electric phaser

ABSTRACT

An exemplary engine assembly includes a crankshaft, and a camshaft having cam lobes mounted thereon. The cam lobes are configured to provide lift to respective devices as a function of a rotation of the camshaft. The cam lobes are circumferentially offset from one another such that a timing of operation of the lift is different for each of the at least two cam lobes. The assembly includes at least one roller bearing coupled to the camshaft, and an electric cam phaser configured to alter the timing of the camshaft with respect to the crankshaft as a function of engine operation.

BACKGROUND

Engine manufacturers are constantly seeking to increase power output andfuel efficiency of their products. One method of generally increasingefficiency and power is to reduce the friction within a camshaft of theengine.

Camshafts are typically used to control valve motion and other importanttiming events in internal combustion engines. The camshaft is a shafthaving axially spaced cams or cam lobes, which project outwardly fromthe surface of the shaft. The shaft and cams can be machined from asingle part and may also be assembled from separate parts. The camshaftis typically supported by bearings, such as journal bearings that arepositioned between the cams along the axial direction of the camshaft.The journal bearings (or fluid film or sleeve bearings) operate by meansof a fluid film of oil, typically fed to the bearings via a pressurizedfeed through drillings in the bearing housing or other routes.

The engine includes a crankshaft that can be directly coupled to thecamshaft using gears, belts, chains, and the like. Thus, the crankshaftis a reference shaft from which timing events are determined for otherengine operations. The camshaft may be independently controlled relativeto the crankshaft to improve engine efficiency. One known device forindependently controlling the camshaft relative to the crankshaft is acam phaser. A cam phaser on a camshaft provides variable camshaftrotation to improve engine timing and lift events, leading to improvedengine efficiency. Overall efficiency is improved at least in partbecause it may be desirable to alter the relative timing between thecamshaft and the crankshaft, depending on the condition of operation ofthe engine. For instance, at idle the relative timing between the twoshafts may have one desired timing, which may differ when the engine isa high speed operation.

Various cam phasing technologies are used to accomplish variable camphasing, including helical spline phasers, hydraulic vane rotor phasers,and cam torque actuated phasers. Variable cam phasing or timingaccommodates the divergent needs for power and torque output, idlestability, fuel economy, and emissions control, as examples. These camphasing technologies require a pressurized oil feed from the enginehydraulic pump for their operation. Because the engine includeshydraulic feed for the bearings, oil from the hydraulic system istypically thereby fed to the cam phaser as well.

The demands on the hydraulic pump for supplying oil to bearings divertpower output away from other engine operations. These parasitic powerlosses reduce the engine's efficiency. The parasitic losses areincreased with the presence of a cam phaser because of its oil feed.Thus, despite improved engine efficiency with the use of variablecamshaft/crankshaft timing, parasitic losses from the cam phaser and thebearings prevent the engine from operating at its peak efficiency.

Accordingly, there is a need for an improved camshaft for an internalcombustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, illustrative examples are shown indetail. Although the drawings represent the exemplary illustrationsdescribed herein, the drawings are not necessarily to scale and certainfeatures may be exaggerated to better illustrate and explain aninnovative aspect of an exemplary illustration. Further, the exemplaryillustrations described herein are not intended to be exhaustive orotherwise limiting or restricting to the precise form and configurationshown in the drawings and disclosed in the following detaileddescription. Exemplary illustrations are described in detail byreferring to the drawings as follows:

FIG. 1 is an exemplary engine assembly;

FIGS. 2A and 2B illustrate exemplary cam lobe profiles that can beincorporated into the engine assembly of FIG. 1; and

FIGS. 3A-3D illustrate exemplary bearing arrangements that can beincorporated into the engine assembly of FIG. 1.

DETAILED DESCRIPTION

Reference in the specification to “an exemplary illustration”, an“example” or similar language means that a particular feature,structure, or characteristic described in connection with the exemplaryapproach is included in at least one illustration. The appearances ofthe phrase “in an illustration” or similar type language in variousplaces in the specification are not necessarily all referring to thesame illustration or example.

In some exemplary illustrations, components of an engine are shown thatincludes a camshaft that is coupled to a crankshaft. The camshaftincludes at least two cam lobes mounted thereon, and the two cam lobesare configured to provide lift to respective devices as a function of arotation of the camshaft. The cam lobes may be circumferentially offsetfrom one another such that a timing of operation of the lift isdifferent for the cam lobes. The camshaft includes at least one rollerbearing coupled to the camshaft. An electric cam phaser is configured toalter the timing of the camshaft with respect to the crankshaft as afunction of engine operation.

Turning now to FIG. 1, an exemplary engine assembly 100 is shown. Engineassembly 100 is an internal combustion (IC) engine according to oneembodiment and a compression ignition (CI) engine according to anotherembodiment. Engine assembly 100 provides motive power to a vehicle suchas a car, truck, bus, etc. However, the applications are not limited tothose listed and may be applicable to any device that may derive motivepower from an engine assembly such as engine assembly 100.

Engine assembly 100 includes a timing input or crankshaft 102 and acamshaft 104 that are coupled to one another via an electric cam phaser106. Crankshaft 102 is configured to rotate in a crankshaft rotationdirection 108 and about a crankshaft rotation axis 110. Crankshaft 102includes a number of elements, not shown, that include but are notlimited to crank throws or crank pins that are radially offset fromcrankshaft rotation axis 110. During rotation, the crankshaft throwsprovide a reciprocating motion to, as one example, pistons withincylinders. The angular orientation of the crankshaft throws, withrespect to one another, controls motion of the pistons with respect toone another. The relative rotation is of the crankshaft throws iscoupled to timing of the combustion events within the cylinders.According to one example, element 102 is simply a timing referencedevice from which timing events in the are determined.

Camshaft 104 includes, in the illustrated example, two cam lobes 112,and camshaft 104 is configured to rotate about a rotational axis 114,independent of rotation 108 of crankshaft 102. Rotational axis 114 isshown to be collinear with rotational axis 110; however, in otherexemplary approaches the two axes 110, 114 are offset from one another.Cam lobes 112 provide mechanical action to devices within engineassembly 100, including but not limited to a valve, an injection pump, avacuum pump, and a fuel pump, as examples. That is, cam lobes 112 areeccentrically shaped or oblong devices that are positioned having aprofile that determines a timing and extent of operation that derivestherefrom and is controllable via the profile.

FIGS. 2A and 2B illustrate exemplary profiles of cam lobes. FIG. 2Ashows a cam assembly 200 having a generally circular cam lobe 202 thatis eccentrically mounted on a rotatable shaft 204. Rotatable shaft 204corresponds to rotational axis 114 of engine assembly 100. Circular camlobe 202 is offset an eccentric distance 206 from a center 208 ofcircular cam lobe 202. As such, when circular cam lobe 202 is caused torotate 210 about rotatable shaft 204 a cam follower 212 is caused tomove axially 214, which causes the mechanical action to the devices asdescribed above.

FIG. 2B shows another example of a cam assembly 250 having an oblonglobe or profile 252 that is mounted to rotatable shaft 204. As such,when oblong lobe 252 is caused to rotate 210 about rotatable shaft 204,a cam follower 254 is caused to move axially 256, which again causes themechanical action to the devices as described above, howevercommensurate with the profile of oblong lobe 252.

As such, referring back to FIG. 1, cam lobes 112 are configured toprovide lift to respective devices as a function of rotation of camshaft104, and cam lobes 112 are circumferentially offset from one anothersuch that a timing of operation of the lift is different for each of theat least two cam lobes. Engine assembly 100 includes bearings 116 thatsupport camshaft 104. And, although two cams 112 and two bearings 116are illustrated, it is contemplated that more cams and bearings may beincluded along camshaft 104.

One or more of bearings 116 coupled to camshaft 104 are roller bearingsand may be, according to illustrative embodiments, a conical rollerbearing, a ball bearing, a needle bearing, and a cylindrical bearing. Inone embodiment, all of bearings 116 on camshaft 102 are roller bearings.The bearings selected typically provide an ability to carry a radialload, but one or more bearings may also be included to also limit axialmotion of the shaft. Roller bearings, as is commonly known, may belightly lubricated with a residual amount of lubricant, but do not havepressurized or replenished oil supply, and there is not pumped oil forlubrication to operate. That is, the roller bearings do not have alubricating oil feed. Contrary to bearings that are typically used for acamshaft, one or all of bearings 116 are roller bearings that operate inan operation that does not include a pressurized oil supply. Further, asillustrated and as discussed, electric cam phaser 106 couples crankshaft102 with camshaft 104.

Electric cam phaser 106 is configured to alter the timing of thecamshaft with respect to the crankshaft as a function of engineoperation. That is, electric cam phaser 106 may be an electric orelectronic device that uses brushless DC electric motors to actuate agear mechanism to effect cam phasing with low power consumption. Assuch, cam phaser 106 does not include an oil feed and thus operates inan oil free mode.

Various bearing and cam phaser arrangements may be incorporated into thecamshaft and in conjunction with an electric cam phaser. FIGS. 3A-3Dillustrate bearing/electric cam phaser arrangements that can beincorporated into engine assembly 100 illustrated in FIG. 1.

Referring to FIG. 3A, bearing/cam phaser assembly 300 includes anelectric cam phaser 302 that is coupled to a camshaft 304, andcoupleable to a crankshaft, such as crankshaft 102 of engine assembly100. Assembly 300 includes cam lobes 306 and roller bearings 308, 310,312, and 314 that operate without an oil feed for lubrication. In theillustrated example, roller bearing 308 is a ball bearing that includesinner and outer races and balls that transmit load on camshaft 304 to asupport structure (not shown) via support frame 316. Roller bearings310-314 are needle bearings that include a relatively large contactsurface compared to ball bearing 308. Needle bearings 310-314 also tendto have a lower profile relative to ball bearing 308 so are morecompact. Needle bearings 310-314 include a needle cage and needlerollers that contact and support camshaft 304 and carry the load ofcamshaft 304 to the support structure via support frames 318. Cam phaser302 may be positioned at a first end 320 of camshaft 304, or mayalternatively be positioned at a second end 322 and coupled to thecrankshaft. Thus, because cam phaser 302 is electric and because all thebearings are roller bearings, there is no need to feed oil to the regionof the cam shaft. This reduces parasitic losses, thereby providing anoverall simpler and more compact engine design as compared to approachespreviously utilized at least in part because the engine oil pump can besmaller, and because there are no oil feed lines to the area of the camshaft.

FIG. 3B illustrates another exemplary bearing/cam phaser assembly 340that includes cam phaser 302 coupled to camshaft 304, cam lobes 306,ball bearing 308, and needle bearing 310. However, in this example twojournal bearings 342 are included that do not include roller elementssuch as in roller bearings 308, 310. Journal bearings 342 includecontact surfaces 344 that slide over camshaft 304. Because of theincreased surface area compared to roller bearings 308, 310, there is anincreased propensity for frictional heating as well during rotation ofcamshaft 304. Accordingly, journal bearings 342 include oil feed lines346 that pass through their respective support frames 348. Thus,although in this embodiment oil feed lines 346 are included to some ofthe bearings (342), the parasitic losses are nevertheless reduced whencompared to a design in which all bearings are journal bearings. Thus,with the combination of the electric cam phaser and some rollerbearings, parasitic losses to the engine are reduced and overall enginedesign is simplified because of a reduced need to provide oil feed toall of the bearings and to the cam phaser.

FIG. 3C illustrates another exemplary bearing/cam phaser assembly 360. Acam phaser assembly 362 provides dual independent control to two shaftsof a camshaft via a first cam phaser 364 and a second cam phaser 366.First cam phaser 364 is coupled to an inner shaft or inner camshaft 368.Second cam phaser 366 is coupled to first cam phaser 364 as well as toan outer shaft or outer camshaft 370 that is radially or concentricallypositioned outside inner shaft 368. Either first cam phaser 364 orsecond cam phaser 366 is also coupleable to a crankshaft (not shown).

Assembly 360 includes cam lobes that are coupled to either inner shaft368 or outer shaft 370. In this example, a cam lobe 372 is mounted orcoupled to inner shaft 368 via a pin 374, and cam lobes 376 are mountedor coupled directly to outer shaft 370. Outer shaft 370 is supported, inthis exemplary approach, by a mix of roller bearings and journalbearings, and inner shaft 368 is supported by first cam phaser 364 on afirst end 378 and a bearing (not shown) on a second end 380. Inner shaft368 and outer shaft 370 are therefore rotatable relative to one anotherby independently controlling each cam phaser 364, 366, relative to eachother. Cam lobe 372 can thereby be rotationally controlled relative tocam lobes 376. Thus, having separate cam phasers enables an additionaldimension of control to the operation of assembly 360.

That is, both cam phasers 364, 366 may be coupled to one another andcoupled to the crankshaft, which directly couples both shafts 368, 370(and their respective cam lobes 372, 376) together and to thecrankshaft. However, cam phasers 364, 366 may be rotated relative to oneanother such that a cam profile of cam lobe 372 can be alteredcircumferentially with respect to cam lobes 376. In such fashion, timingof lift events within assembly 360 may be further controlled by alteringrotation of both shafts 368, 370 relative to the crankshaft, and byaltering rotation of both shafts 368, 370 relative to each other.

As stated, referring still to FIG. 3C, outer shaft 370 is supported by amix of roller bearings and journal bearings. Thus, in the example shownball bearing 382 and needle bearing 384 are included, while oil-fedbearings 386 are shown having oil feed lines 388.

Similarly, FIG. 3D shows an exemplary assembly 394 having cam phaserassembly 362 that enables relative motion between shafts 368, 370 andwith respect to the crankshaft. However, in this example all bearingsoperate without an oil feed for lubrication. As shown in FIG. 3C, rollerbearing 382 and needle bearing 384 are shown, but assembly 394 of FIG.3D includes needle bearings 396 as well. Thus, because cam phaserassembly 362 is electric and because all the bearings are rollerbearings, there is no need to feed oil to the region of the cam shaft.This reduces parasitic losses and providing an overall simpler and morecompact engine design because the engine oil pump can be smaller, andbecause there are no oil feed lines to the area of the cam shaft.

Thus, in the examples illustrated, cam shaft operation may be controlledwith respect to the crankshaft operation, and lobes within the camshaftmay be controlled with respect to one another via an electric phaserassembly having one phaser coupled to one shaft, and another phasercoupled to another shaft (cam-in-cam). Further, both operations arepossible and in the concentric camshaft arrangement shafts may becontrolled with respect to one another and operation of both iscontrolled with respect to the crankshaft. As such, the amount of oilfed to the engine is reduced and there is no need for oil or hydraulicfluid for a phaser. In addition, aside from the reduced parasiticlosses, there is no need for a rotating coupler for putting oil into thecamshaft (such as, for a slide or journal bearing). As a result, fewerengine components are required along with the lack of need for phaseractivation. Moreover, the engine oil pump may be reduced in size.

With regard to the processes, systems, methods, heuristics, etc.described herein, it should be understood that, although the steps ofsuch processes, etc. have been described as occurring according to acertain ordered sequence, such processes could be practiced with thedescribed steps performed in an order other than the order describedherein. It further should be understood that certain steps could beperformed simultaneously, that other steps could be added, or thatcertain steps described herein could be omitted. In other words, thedescriptions of processes herein are provided for the purpose ofillustrating certain embodiments, and should in no way be construed soas to limit the claimed invention.

Accordingly, it is to be understood that the above description isintended to be illustrative and not restrictive. Many embodiments andapplications other than the examples provided would be upon reading theabove description. The scope of the invention should be determined, notwith reference to the above description, but should instead bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled. It isanticipated and intended that future developments will occur in the artsdiscussed herein, and that the disclosed systems and methods will beincorporated into such future embodiments. In sum, it should beunderstood that the invention is capable of modification and variationand is limited only by the following claims.

All terms used in the claims are intended to be given their broadestreasonable constructions and their ordinary meanings as understood bythose skilled in the art unless an explicit indication to the contraryin made herein. In particular, use of the singular articles such as “a,”“the,” “said,” etc. should be read to recite one or more of theindicated elements unless a claim recites an explicit limitation to thecontrary.

What is claimed is:
 1. An engine assembly comprising: a crankshaft; acamshaft having at least two cam lobes mounted thereon, the at least twocam lobes configured to provide lift to respective devices as a functionof a rotation of the camshaft, wherein the at least two cam lobes arecircumferentially offset from one another such that a timing ofoperation of the lift is different for each of the at least two camlobes; at least one roller bearing coupled to the camshaft; and anelectric cam phaser configured to alter the timing of the camshaft withrespect to the crankshaft as a function of engine operation.
 2. Theengine assembly of claim 1, wherein the at least one roller bearing isone of a conical roller bearing, a ball bearing, a needle bearing, and acylindrical bearing.
 3. The engine assembly of claim 1, wherein at leastone of the roller bearings coupled to the camshaft operates without alubricating oil feed.
 4. The engine assembly of claim 3, wherein all ofthe roller bearings coupled to the camshaft do not have a lubricatingoil feed.
 5. The engine assembly of claim 1, wherein: the camshaft iscomprised of an inner shaft and an outer shaft that is outside the innershaft; one of the at least two cam lobes is mounted to the inner shaft;another of the at least two cam lobes is mounted to the outer shaft; andthe electric cam phaser is a cam phaser assembly that provides dualindependent control and is configured to rotate the inner shaft withrespect to the outer shaft.
 6. The engine assembly of claim 1, whereinthe respective devices are one of a valve, an injection pump, a vacuumpump, a fuel pump, or other actuated device.
 7. The engine assembly ofclaim 1, wherein the engine assembly is one of a spark ignition (SI)engine and a compression ignition (CI) engine.
 8. A method ofmanufacturing an engine, comprising: providing a crankshaft; providing acamshaft having multiple lobes configured to provide mechanical actionto respective devices as a function of a rotation of the camshaft,wherein the at least two cam lobes are circumferentially offset from oneanother such that a timing of operation of the mechanical action isdifferent for at least two of the multiple cam lobes; coupling at leastone roller bearing to the camshaft; coupling an electric cam phaserbetween the camshaft and the crankshaft; and configuring the electriccam phaser to alter the timing of the camshaft with respect to thecrankshaft as a function of engine operation.
 9. The method of claim 8,wherein coupling at least one roller bearing to the camshaft comprisescoupling one of a conical roller bearing, a ball bearing, a needlebearing, and a cylindrical bearing.
 10. The method of claim 8, whereincoupling the at least one roller bearing to the camshaft comprisescoupling at least one of the roller bearings to the camshaft that doesnot have a lubricating feed.
 11. The method of claim 8, wherein couplingthe at least one roller bearing to the camshaft comprises couplingroller bearings to the camshaft that are all without a lubricating feed.12. The method of claim 8, wherein: providing the camshaft comprisesproviding an inner shaft concentrically placed within an outer shaftsuch that both inner and outer shafts rotate with respect to a centralrotation axis; and further comprising: mounting one of the at least twocam lobes to the inner shaft; mounting one of the at least two cam lobesto the outer shaft; and wherein configuring the electric cam phaserfurther comprises configuring the electric cam phaser assembly toprovide dual acting control and to rotate the inner shaft with respectto the outer shaft.
 13. The method of claim 8, wherein providing thecamshaft to provide the mechanical action further comprises providingthe camshaft to provide the mechanical action to the respective devicesthat are one of a valve, an injection pump, a vacuum pump, and a fuelpump or other actuated device.
 14. The method of claim 8, wherein theengine is one of a spark ignition (SI) engine and a compression ignition(CI) engine.
 15. A camshaft assembly comprising: a camshaft having atleast two cam profiles positioned along respective axial locations, theat least two cam profiles configured to provide lift to respectivedevices of an engine, wherein the at least two cam profiles arecircumferentially offset from one another such that a timing ofoperation of the lift is different for each of the at least two camprofiles; and at least one roller bearing coupled to the camshaft; anelectric cam phaser coupled to the camshaft and coupleable to acrankshaft, the electric cam phaser configured to alter the timing ofthe camshaft with respect to the crankshaft as a function of engineoperation.
 16. The camshaft assembly of claim 15, wherein the at leastone roller bearing is one of a conical roller bearing, a ball bearing, aneedle bearing, and a cylindrical bearing.
 17. The camshaft assembly ofclaim 15, wherein at least one of the roller bearings coupled to thecamshaft does not have a lubricating oil feed.
 18. The camshaft assemblyof claim 17, wherein all of the roller bearings coupled to the camshaftdo not have a lubricating oil feed.
 19. The camshaft assembly of claim15, wherein: the camshaft is comprised of an inner shaft and an outershaft that is outside the inner shaft; one of the at least two camprofiles is mounted to the inner shaft; another of the at least two camprofiles is mounted to the outer shaft; and the electric cam phaser isan electric cam phaser assembly that provides dual independent controland is configured to rotate the inner shaft with respect to the outershaft.
 20. The camshaft assembly of claim 15, wherein the respectivedevices are one of a valve, an injection pump, a vacuum pump, and a fuelpump or other actuated device.